1. Field of the Invention
The present invention relates to an eco-run control device that has an eco-run function to drive a vehicle while starting and stopping the engine.
2. Description of the Related Art
In recent years, to improve fuel efficiency and reduce emission, eco-run control devices are mounted on vehicles. An eco-run control device issues an engine stop instruction when predetermined engine stop requirements are satisfied, and later issues an engine restart instruction to drive an engine starting motor when predetermined engine start requirements are satisfied.
An eco-run ECU that performs eco-run control operations determines whether to stop the engine and whether to start the engine, based on an eco-run allowing signal and an eco-run prohibiting signal transmitted from another ECU, and signals transmitted from various sensors and actuators.
An eco-run ECU and most ECUs cooperating with the eco-run ECU form a so-called IG system, and power is supplied to the ECUs when the ignition switch is switched on. In the IG system, when the ignition key is turned off, the power supply to the ECU is cut off, and the ECUs are put into a reset state. However, data needs to be written in a nonvolatile memory in the eco-run ECU, and therefore, the eco-run ECU has a main relay so that an operation can be continued for a predetermined period of time (approximately 3 seconds) after the ignition key is turned off.
When the driver switches the ignition key from an ON state to an OFF state to an ON state in a short period of time during an eco-run control operation, the eco-run ECU is not reset, but the other ECUs are reset. Therefore, the other ECUs transmit an eco-run prohibiting signal to the eco-run ECU when the ignition key is switched from an OFF state to an ON state.
The eco-run ECU that has received the eco-run prohibiting signal drives the starter motor in accordance with the eco-run prohibiting signal. In other words, the starter driving is performed, with the switching of the ignition key from an OFF state to an ON state being a trigger. As a result, the starter driving is automatically started, even though the driver does not operate to turn on the starter motor. This makes the driver feel uneasy. In the worst case, the vehicle suddenly moves forward.
To counter such a problem, the RAM in the eco-run ECU is pseudo-reset by software. The RAM is reset when the ignition key is in an OFF state and an interruption is detected in a communication of one of the ECUs communicating with the eco-run ECU. The ECUs that communicate with the eco-run ECU may be any ECUs among the ECUs connected to an IG line, the ECUs connected to an accessory power supply line, and the ECUs connected to a +B line. The IG line is the power supply line connected to the +-pole of the battery via the ignition switch. The accessory power supply line is the power supply line connected to the +-pole of the battery via an accessory switch. The +B line is the power supply line connected directly to the +-pole of the battery.
Japanese Unexamined Patent Publication No. 2004-17676 discloses a technique by which a control device that is connected to a network and has an error is restarted and is put back into an initialized state when the error is caused.
By a conventional method for resetting an eco-run ECU, the eco-run ECU is reset when a communication between the eco-run ECU and an ECU connected to the +B line or the ACC line is interrupted. By this method, the IG switch is determined to be OFF due to an inadvertent key operation, when a communication with another ECU is interrupted due to disconnection or temporary disconnection of the IG line. In such a case, the RAM of the eco-run ECU is reset, so as to prohibit the eco-run ECU from performing an engine start control operation, or to stop the engine.
In communications between the eco-run ECU and the other ECUs, the compensation for a low voltage is 8 V or higher. Therefore, when the IG line is temporarily disconnected at the time of a low voltage, communications might become invalid. Accordingly, there is a possibility that the eco-run ECU is frequently reset when the voltage is low.
Japanese Unexamined Patent Publication No. 2004-17676 does not disclose a method for determining whether the ignition switch is switched off by an operation of the ignition key or temporary disconnection of the IG line.